BG64866B1 - Mineral flaky filler for composites - Google Patents

Abstract

A mineral flaky filler for composites, produced by melting a starting mineral, shaping hard flaky vitreous particles from melt, and subjecting such particles to thermochemical treatment in an oxidizing atmosphere until a crystal phase is developed. With an object of obtaining such a crystalinity-reactivity balance that would provide for quality consistant protective and ornamental coating on large-size articles and structures preferably for use in the tropical climate and of producing a filler that would be commercially available at the step of the thermochemical treatment the flaky particles were treated at a temperature range from 680 to 850 degrees C until at least 12 % by weight the crystal phase and at least 7x1019 spin/cm3 of reactive paramagnetic centres were developed, and followed by air cooling.

Description

The invention relates to dispersed flakes of uncertain chemical composition, which can be prepared from minerals containing lower iron oxides (preferably basalt, sand sands, etc.) by melting these minerals, dispersing the melt to produce glass. solid flakes and subsequent chemical modification and partial crystallization of the material from these flakes by thermochemical treatment in an oxidizing gas environment.

It is widely known that such flakes are useful as chemically active fillers for a variety of composite materials (preferably polymerizable composite materials) for the preparation of protective and protective-decorative coatings with high atmospheric and water resistance properties (in the protection of metal tanks, bridges, offshore drilling rigs, etc.) and / or abrasion resistance (eg sludge and slurry pipelines).

BACKGROUND OF THE INVENTION

As is clear from the field of application, the need for such fillers is considerable. Accordingly, they must meet a set of precise and difficult-to-comply requirements, the most important of which are:

- the highest possible chemical activity, evaluated at least by their relative surface area, and preferably by the presence of active centers on the surface of the flakes, which centers assist in the polymerization of various oligomeric binders and in the formation of chemical bonds between the macromolecules of the polymer and inorganic components;

- the highest possible mechanical resistance, which causes a significant reinforcing effect in the finished composite materials, even at low concentration of flake fillers;

- the highest possible chemical stability (and especially corrosion resistance), facilitating the storage of the fillers and their use in the composition of many composite materials whose starting non-cured mixtures typically contain corroding ingredients;

- accessibility for a wide range of users, which is determined by the mass production capability and the cost of resources.

Taken individually, these requirements are not difficult to achieve.

For example, from lit. source [1] as available and chemically active filler for polymerizable composite materials are known glass flakes with an average thickness of 0.5-5.0 pm and a diameter of 100400 pm and a mixture containing from 10 to 70 parts by weight of such flakes and from 10 to 150 parts by weight of flake metal pigments.

The disadvantage of this filler is that the glass flakes are usually not sound, their surface chemical activity without further treatment (eg vacuum metallization) is low, and metal flakes with a high relative surface are susceptible to corrosion.

Scaly fillers of the type of artificial mica iron pigments lit are also known. source [2]. Compared to glass flakes, they are more durable and chemically resistant. Their disadvantage is that they are expensive, so their use is justified only in the application of protective coatings to such products and equipment, in which the losses from their accident greatly exceed the cost of protection.

Therefore, one of the most preferred directions for the production of flake fillers for predominantly polymeric composite materials is the use of natural minerals.

Thus, with the participation of the inventor of the present invention, a known technological complex using basalt has been developed, which includes:

- a method for the production of fine flake particles [3],

a device for the production of fine flake particles [4] and

- a method for heat treatment of dispersed flake particles and a device for its realization [5].

The mineral flake filler according to lit. source [3] was obtained by melting the balloon and dispersing the melt in the form of elliptical flakes. Their coefficient of deviation from the correct circle, calculated from the results of microscopic examinations of their shape and size, such as the ratio of the small and large axes of the ellipse, ranges from 0.80 to 0.95.

The disadvantage of this vitreous flake material is that it is chemically unstable due to the presence of lower iron oxides in the basalts (and sand dunes). In addition, the flakes have low chemical activity.

The mineral flake filler according to lit. the source [4] was obtained by the same method and compared to the filler described above it has only a suitable particle size distribution, namely it contains up to 99% flakes of practically the same shape and size. Its disadvantage is that the vitreous structure, chemical instability and low chemical activity persist.

These deficiencies are largely eliminated in the mineral filler of lit. source [5], which is closest to the one proposed by its technical nature.

It is obtained by melting the starting material (basalt), forming from the molten solid glassy flake particles and thermochemical treatment of such particles in an oxidizing gas environment to obtain a predominant crystalline structure, which treatment involves heating the glassy particles at a rate of 40 to 90 ° C / mm to temperatures in the range of 600-950 ° C with simultaneous purging with air for 5 to 30 min and subsequent forced cooling at a rate of not less than 950 ° C / min. After such treatment, the mineral flake filler is substantially free of FeO and is characterized by a high (3 g / cm ² or more) density that exceeds the glass particle density of at least 1.5 times, a high proportion (53% and more) of crystalline phase (hereinafter referred to as the "degree of crystallinity") and a significant amount of chemically active paramagnetic centers (hereinafter referred to as PMC).

The aforementioned advantages make it possible to significantly improve the properties of the polymerizable composite materials containing the described mineral flake filler and the protective and protective coatings obtained therefrom [6].

However, the disadvantage of this filler has been found to be no more than 6 x 10 ”spin / cm ³ active in the polymerization processes of mono / oligomeric CMCs [7]. In other words, said crystallinity and chemical activity of the known filler are "unbalanced".

In addition, experimental studies have shown that the pursuit of the highest possible crystallinity of the mineral flake filler is also unjustified from a technological point of view. Such thermochemical treatment for 30 min at temperatures selected at the beginning of said interval (i.e., slightly higher than 600 ° C) provides neither a noticeable crystallization nor a noticeable increase in chemical activity, and an increase in the treatment duration over 30 min substantially reduces the productivity of the process. The transition to relatively short-term (for example - 10-15 min) thermochemical treatment at temperatures above and above 900 ° C results in (as it turned out, unexpected) uncontrolled crystallization (return to glassy state) of the particles and their chemical reduction. activity, which is as high as the higher the temperature for heating the starting particles and the faster the cooling of the treated particles. It is also made clear that the heating rate of the source glass particles until they are brought into contact with the gaseous oxidizer (air) does not in practice affect the flow and the result of the thermochemical treatment and, therefore, the use of additional control and regulation apparatus for these purposes is unjustified. makes the product more expensive.

SUMMARY OF THE INVENTION

It is an object of the invention, in connection with the foregoing, to create such a mineral flake filler for composite materials that is substantially "balanced" in terms of the degree of thermal expansion of the thermochemical treatment modes of the glassy flake particles and their subsequent cooling. crystallinity and, by its chemical activity, more accessible to the consumer, the use of which ensures the receipt of salutary protective and protective-decorative or wear-resistant coatings of polymerizable composite materials. Terry.

The mineral flake filler for composite materials is obtained by melting the starting material, the formation of solid flaky glassy particles from the melt and their thermochemical treatment in an oxidizing gas medium to obtain a crystalline phase, according to the invention the thermochemical treatment is carried out at a temperature in the range from 680 to 850 ° C to achieve not less than 12% by weight of the crystalline phase and more than 7 x 10 ¹⁹ spin / cm ³ reactive CMCs, followed by air cooling.

The advantage of this filler is that it is mechanically stable due to the appropriate degree of crystallization. Due to the harmonic combination of crystallization rate and chemical activity, it can serve as a highly effective means of enhancing the quality of mostly thick (> 1 mm, most often> 3 mm) protective, protective-decorative and wear-resistant coatings using such binders formed during the polymerization of mono- and / or oligomers.

Another advantage is that in the production of the proposed filler, both the costs of heating and cooling equipment and the management of these processes are reduced, as well as the operating energy costs of thermochemical treatment and preparation and delivery of the refrigerant. This makes the product more accessible to consumers.

An additional advantage is that the mineral flake filler has at least 30% by weight particles with a mean cross-section of about 100 pm and more than 7 x 10 ”spin / cm ³ PMC, which is preferable when using the product in polymerizable composite materials .

An exemplary embodiment of the invention

The essence of the invention is further explained by:

- a general description and specific data for the implementation of the method of production of the proposed mineral flake filler for polymerizable composite materials with an exposure to the physicochemical properties achieved therein;

- Examples of the use of the filler in polymerizable composite materials for protective coatings and the results of comparative tests of composite materials for such coatings.

In general, the method of producing the proposed mineral flake filler involves the following steps:

(1) production of solid glassy particles (usually in the form of flakes) by:

- crushing the selected material into pieces of a size suitable for feeding into a melting furnace;

- heating these pieces to obtain a molten melt (in particular, to temperatures of 1400-1500 ° C for basalt and above 1500 ° C for sand sands);

- the formation of glassy particles by dispersing (for example, a turbine and / or airflow) the molten jets flowing through a heated nozzle;

(2) thermochemical treatment of the raw material obtained in step (1) in an oxidizing gas medium (preferably air) at a temperature of from 680 to 850 ° C (preferably 680780 ° C) to partially crystallize the material and obtain a crystalline phase not - less than 12% by weight and more than 7 x 10 ”spin / cm ³ chemically active PMCs with subsequent air cooling; and if desired;

(3) machining (eg, crushing and particle sorting) to obtain a mineral flake filler with at least 30% by weight of particles having an average transverse size of 100 pm and to obtain more than 14 x 10 ”spin / cm ³ chemically active PMCs

Basalt from the Kostopol (Ukraine) deposit containing about 10% FeO was used for the preparation of hard glassy flakes. Basalt gravel (crusher) of size 5 to 10 mm is melted in a modified melting furnace, similar in design to quartz glass furnaces, using gas burners. The melt is heated to temperature

1400-1500 ° C and is fed through a heated nozzle of 8 to 10 mm. The melt stream is dispersed through the turbine at a temperature of about 1300 ° C in the stream of cooling air.

The resulting flakes are gray in color, about 3 pm thick and 25 pm in diameter, preferably 3 mm. They are carefully (in order to avoid breaking and sealing them) poured into porous layers 80-100 mm thick in heat-resistant steel troughs and subjected to thermochemical treatment in air in a muffle furnace at temperatures of 660,680, 750, 850 and 875 ° C for 90, 60, 30, 20 and 15 min respectively, after which they are removed from the oven and cooled to ambient air.

Samples of treated flakes at the temperatures described were examined by conventional methods for the degree of crystallization and the amount of PMC.

The degree of crystallization X is determined by the formula:

X KF ^ SF x 100% where d ₀₄ is the density of the treated particles, d _C4 is the density of the original glassy particles, d _{K (t>} is the density of the crystalline phase, d _C0 is the density of the glassy phase, as a result of the pycnometric determination of the values of the densities in xylene [8].

The amount of PMC is determined by comparing the electron-paramagnetic resonance (EPR) spectra of the mineral filler and dipanylpicrylhydrazine as a reference substance [9]. The EPR spectra were determined using a radio spectrometer model E / x-2547 of 20 Radioplan (Poland). The results of the measurements are summarized in Table 1.

Table 1.

Crystalline phase concentration and paramagnetic centers depending on the temperature of the thermochemical treatment.

Metrics * The temperature of the thermo-chemical treatment 660 ° C 680 ° C 750 ° C 850 ° C 875 ° C The degree of crystallinity,% by weight 5.8 14,8 35D 52,3 49,8 Amount of PMC 10 '* spin / cm ³ 5.8 16 18 19 17

* 3Note: the same values for the original glassy particles are 0.0% and <2.0 x 10 ”spin / cm ³ , respectively, and for the filler prototype particles obtained by thermochemical treatment at 900 ° C to a virtually complete transition of FeO in Fe ₂ O ₃ , respectively - 51.5% and about 6.0 x 10 ”spin / cm ³ .

As can be seen from Table 1, the thermochemical treatment of the glassy particles is impractical both at temperatures below 680 ° C, as the crystallinity and the amount of PMC increase slightly and at temperatures above 850 ° C when they start, 45 though insignificant, they get worse.

After thermochemical treatment, the mineral flake filler is crushed and sorted granulometrically to increase its chemical activity. Particles obtained by thermochemical treatment at 750 ° C are used. Samples of different particle contents with a mean cross section of 100 µm were prepared and the amount of PMCs determined and the results are given in Table 2.

Table 2.

Concentration of paramagnetic centers depending on the average particle size of the sample.

Percentage of medium sized particles <100 pm 5.0 10,0 20,0 30.0 40,0 80,0 The amount of PMC, IU ¹ 'spin / ush ³ 90 210 280 370 560 630

To assess the effect of the mineral flake filler on the physico-mechanical properties of the polymerizable composite materials, standard specimens were prepared to determine the adhesive strength (measured as the force required to tear off a steel sponge slice from a coating deposited on a steel substrate). the tensile strength of the bending and tensile forces, the modulus of elasticity in lateral bending and the relative toughness (tensile strength). Similar specimens of the known prototype filler were tested by the same methods (the methods and equipment for these tests are well known to those skilled in the art).

For these tests, a filler according to the invention (PI) was obtained, obtained by thermochemical treatment at 680 ° C, not fragmented and unsorted in particle size and therefore having minimum values of crystallinity and the amount of PMC. As a filler prototype (PP), a material obtained at 900 ° C and having close to the maximum crystallinity and amount of PMC was used. A relatively simple mixture of acrylic monomers containing polymer additives and a radical polymerization initiator, the composition of which is given in the left column of Table 3, was used as a binder in the cold-cured experimental polymerizable composite materials.

Table 3.

Composition of experimental polymerizable composite materials.

Ingredients Type and number of standard or specifications Quantity in wt. hours Methacrylamide GOST 20370-74 100 Polybutyl methacrylate TU 6-01-358-75 20 Polyvinyl chloride OCT 6-01-37-88 20 Polyisocyanate TU 113-03-29-6-84 15 Benzoyl peroxide * GOST 2168-83 10 * Dimethylaniline GOST 14888-78 3 Filler PI, or Filler PP 10 10

* 3Note: Benzoyl peroxide is used as a paste mixed with dimethyl phthalate in a weight ratio of about 1: 1.

The mixtures for the samples were prepared by dosing the ingredients, pre-mixing methyl methacrylage, polybutyl methacrylage and polyvinyl chloride, adding one of said fillers by mixing, adding polyisocyanate and dimethylaniline also by mixing, and finally adding benzo peroxide. After good mixing, samples sufficient to obtain data on the physico-mechanical properties of the composite material are obtained in a standard manner, with a standard deviation of not more than +/- 5%. The results of the studies are given in Table 4.

Table 4.

Results of comparative studies of materials.

As can be seen from Table 4, the proposed mineral flake filler is more effective in

Properties Filler PI pp Adhesive strength, MPa 42.0 27.0 Boundary strength of shrinkage, MPa 92,0 72,0 Tensile strengths, MPa 14,0 9.2 Side flexural modulus, MPa 36,4 28.5 Impact strength, kJ / m ² 17.3 14.2

comparison with the known prototype filler.

Industrial applicability

The industrial applicability of the proposed mineral flake filler is made clear by the foregoing, both in terms of its mass production potential and its wide scope of application.

Claims

Claims (3)

1. A mineral flake filler for composite materials obtained by melting a parent mineral, the formation of solid flake glass particles by melt and their thermochemical treatment in an oxidizing gas medium to obtain a crystalline phase, characterized in that it is obtained by thermochemical treatment temperature in the range from 680 to 850 ° C to achieve not less than 12 wt. % crystalline phase and more than 7 χ 10 ¹⁹ spin / cm ³ chemically active paramagnetic centers and subsequent air cooling. Mineral flake filler according to claim 1, characterized in that it contains not less than 30% by weight. % of the total mass of the particles with an average transverse size of about 100 µm of the total mass of the particles and a concentration of paramagnetic centers of not less than 14 x 10 spin / cm ³ . Mineral flake filler according to claim 1, characterized in that the starting mineral is, for example, basalt or sand sands.